ITN Speeds

The ITN Road Speeds tab allows you to create an expression for routing based on road-speed values.

Select Applications > Routing Tools > Settings > ITN Speeds.

In SIS Desktop all ITN routes are held as topological links with a DescriptiveTerms$ attribute:

  • Attribute Name: DescriptiveTerms$
  • Sample list of Values: 'Minor Road', 'Local Street', 'B Road', 'A Road', 'Motorway', 'Pedestrianised Street', 'Alley', 'Private Road - Restricted Access', 'Private Road - Publicly Accessible', 'Ferry', 'Footpath'.

These are used for the basis of speed-based routing,

For instance the routing expression embedded within ITN tools looks at the value of DescriptiveTerms$ for each link and assigns the speed defined in the Routing tools settings dialog.

In the example above, routing would be based on a speed of 60mph for each link classed as a Motorway, 30mph for each link classified as an A Road etc. The length of each link is taken from the link itself (i.e. from the ITN coordinates used to create the link).

To include any road classification in the routing expression check the Use tickbox.

Sets of speeds can be saved as custom configurations. For instance to save a set of ‘Normal’ speeds, enter them in the road speed boxes and ensure the tickbox is checked.

Now enter a name in the box next to Save, e.g. Normal, and click Save. Any number of sets (configurations) can be saved.

To load a saved configuration, select it from the drop-down box and click Recall. The speeds are displayed in the road classification boxes; they will be used by subsequent routing operations if the ITN Road Speeds tab is chosen.

To edit a saved configuration, select it from the drop-down box and click Recall. Make the necessary changes, enter the same name of ‘Saved Speed Configuration’ and click Save. The new changes will simply be overwriteen on the old configuration set.

To permanently delete a saved configuration display the name of the configuration in the Recall drop-down box and click Delete.

Click Show ITN Expression to open the expression window. You can copy this expression:

  • into a text editor and customise it as an ‘Own expression’ (e.g. ITN expression can be modified to allow for combinations of DescriptiveTerm$ and NatureOfRoad$ to have different speeds for Single and Dual Carriageway A Roads and B Roads).
  • into core SIS commands wanting an expression
  • when using Workload Modeller